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\f0\b\fs24 \cf0 In Extreme Weather, More Sign of Human Fingerprints\
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\b0 \cf0 Sept. 30, 2014 - Climate change greatly increased the risk of heat waves in 2013, and likely influenced the severity of other extreme weather such as droughts, heavy rains and storms, according to an annual assessment released Monday that aims to track human fingerprints on our changing weather.\
The extremely warm year observed over Australia and the western Pacific, for instance, was "largely attributable to human forcing" of the climate system, the report found. Likewise, the odds of the large-scale atmospheric patterns forming that set California up for its extraordinary drought \'96 the driest-12 month period on record that occurred during 2013 and 2014 \'96 was "very likely increased" by rising human emissions.\
But in a sign of the challenges scientists face in teasing out and attributing the various factors influencing extreme weather, scientists said natural variability likely played a much larger role in other extreme weather seen in 2013, such as the October blizzard in North Dakota, the extreme rains across India in June, and the unusually wet winter in Europe.\
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\i \cf0 Every Event Raises Questions\
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\i0 \cf0 The report, \'93Explaining Extreme Events of 2013\'94, was published by the American Meteorological Society. It is the 3rd year the society has tried to assess how or whether human-driven climate change has contributed to increased likelihood or intensity of extreme events in the previous year.\
"Every extreme event raises questions about how anthropogenic climate change affected its intensity and its probability of occurrence," the authors wrote in their report. "This question arises for many reasons, but often it is the implications for the future that is of greatest concern.\
The 108-page report is the product of more than 91 scientists from institutions worldwide, writing 22 studies on 16 extreme events across the globe. 3 years ago, the report looked at 6 events.\
The science of attribution remains challenging, the authors acknowledged. Even this year's expanded effort represents a "small and non-random sampling" of extreme weather events, they noted.\
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\i \cf0 Patterns Emerge\
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\i0 \cf0 But patterns are starting to emerge: in some cases, human-driven climate change has made the likelihood of a heat wave 10 times greater, as found in Korea last summer. Meanwhile, not surprisingly, the odds of a cold snap are becoming "much less likely."\
On the other hand, severe downpours \'96 and the opposite, a lack of rain \'96 are much harder to attribute to rising global emissions. "A failure to find anthropogenic signals for several events examined in this report does not prove anthropogenic climate change had no role to play," the authors cautioned.\
"The challenges in event attribution are high, both from a technological perspective of improving scientific knowledge and from a communication perspective of explaining what that science knowledge means."\
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\cf0 www.dailyclimate.org/tdc-newsroom/2014/09/extreme-weather-2013}